An image sensor is an electronic device that converts light (in the form of an optical image) into electronic signals. Semiconductor based image sensors have become ubiquitous in modern electronic devices such as cell phones, portable cameras, and desktop/laptop computers. Modern image sensors are generally semiconductor charge-coupled devices (CCD), active pixel sensors in complementary metal-oxide-semiconductor (CMOS), or N-type metal-oxide-semiconductor (NMOS) technologies. Typically these devices are used to capture visible light; however, in certain applications detection of light outside of the visible spectrum is desirable.
Infrared (IR) light is one part of the electromagnetic spectrum. All objects emit some amount of black body radiation as a function of their temperature. Generally, the higher the object's temperature, the more IR light is emitted as black-body radiation. An image sensor made to detect IR works even in total darkness because no ambient light is required. Accordingly, an IR image sensor may be helpful in rescue operations, night time photography, and other dark conditions.
Even more useful than an image sensor that can only detect infrared light, is an image sensor that can detect both IR and visible light. However, detection of infrared light generally requires low-band gap materials that are difficult to integrate with traditional image sensor fabrication processes. Accordingly, it has proved challenging to merge infrared and visible imaging technologies. This difficulty in fabricating hybrid visible-IR image sensors has resulted in hybrid sensors that suffer from low IR sensitivity, visible light contamination, semiconductor defects, and the like.